Pseudomonas syringae pv. tomato type III effectors AvrPto and AvrPtoB promote ethylene-dependent cel

Pseudomonas syringae pv. tomato type III effectors AvrPto and AvrPtoB promote ethylene-dependent cel

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Pseudomonas syringae pv. tomato type III effectors AvrPto and AvrPtoB promote ethylene-dependent cell death in tomato Jonathan R. Cohn 1 and Gregory B. Martin 1,2,* 1 Boyce Thompson Institute for Plant Research, Tower Rd, Ithaca, NY 14853-1801, USA, and 2 Department of Plant Pathology, Cornell University, Ithaca, NY 14853-4203, USA Received 30 June 2005; accepted 8 July 2005. * For correspondence (fax þ 1 607 255 6695; e-mail gbm7@cornell.edu). Summary The type III secretion system (TTSS) of Pseudomonas syringae pv. tomato ( Pst ) injects into the plant cell effector proteins that play an essential role in the formation of bacterial speck disease. To investigate the molecular roles of TTSS effectors in disease formation, we used a cDNA microarray to analyze the expression of approximately 8600 random tomato genes in response to wild-type Pst strain DC3000 and a mutant lacking a functional TTSS. Many of the differentially expressed genes identiFed encode proteins associated with hormone response or hormone biosynthesis pathways. Using isogenic mutant strains of DC3000, we monitored host transcriptional changes in response to the TTSS effector proteins AvrPto and AvrPtoB, both of which are important virulence factors on susceptible tomato lines. We found that AvrPto and AvrPtoB induce a set of host genes involved in ethylene biosynthesis and signaling, and in particular they regulate the expression of two genes, LeACO1 and LeACO2 , encoding the ethylene-forming enzyme ACC oxidase. Analysis of transgenic tomato lines with diminished ACC oxidase activity revealed that ethylene production by the host is required for the full virulence activity of both AvrPto and AvrPtoB. AvrPto and AvrPtoB therefore appear to promote enhanced disease in tomato leaves, in part, by upregulating genes involved in ethylene production. Keywords: disease susceptibility, ethylene, tomato, Pseudomonas . Introduction Many phytopathogenic bacteria employ a specialized type III secretion system (TTSS) to deliver ‘effector’ proteins critical to pathogen virulence into host cells (Alfano and Collmer, 2004). Pseudomonas syringae pv. tomato ( Pst ) strain DC3000, a pathogen of both tomato and Arabidopsis, requires a functional TTSS for growth and disease formation on host plants. DC3000 has been widely used as a model organism for studying molecular aspects of plant–pathogen interactions. Recent completion of the DC3000 genome se- quence revealed the presence of over 20 TTSS effector genes (Buell et al. , 2003; Fouts et al. , 2002; Guttman et al. , 2002). Initially, TTSS effectors from plant pathogens were identi±ed based on their ability to act as avirulence factors that elicit defense responses on host plants expressing a corresponding resistance ( R ) gene (Cohn and Martin, 2003). For example, effectors AvrPto and AvrPtoB both serve as avirulence factors in an incompatible interaction with tomato plants expressing the R gene Pto (Kim et al. , 2002; Pedley and Martin, 2003; Ronald et al. , 1992). Although the role of effectors as avirulence factors has been intensively investigated, only recently has attention been focused on the
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 16

Pseudomonas syringae pv. tomato type III effectors AvrPto and AvrPtoB promote ethylene-dependent cel

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online